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[PATCH] uml: clean arch_switch usage

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Call arch_switch also in switch_to_skas, even if it's, for now, a no-op for
that case (and mark this in the comment); this will change soon.

Also, arch_switch for TT mode is actually useless when the PT proxy (a
complicate debugging instrumentation for TT mode) is not enabled.  In fact, it
only calls update_debugregs, which checks debugregs_seq against seq (to check
if the registers are up-to-date - seq here means a "version number" of the
registers).

If the ptrace proxy is not enabled, debugregs_seq always stays 0 and
update_debugregs will be a no-op.  So, optimize this out (the compiler can't
do it).

Also, I've been disappointed by the fact that it would make a lot of sense if,
after calling a successful
update_debugregs(current->thread.arch.debugregs_seq),
current->thread.arch.debugregs_seq were updated with the new debugregs_seq.
But this is not done.  Is this a bug or a feature?  For all purposes, it seems
a bug (otherwise the whole mechanism does not make sense, which is also a
possibility to check), which causes some performance only problems (not
correctness), since we write_debugregs when not needed.

Also, as suggested by Jeff, remove a redundant enabling of SIGVTALRM,
comprised in the subsequent local_irq_enable().  I'm just a bit dubious if
ordering matters there...

Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Acked-by: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Paolo 'Blaisorblade' Giarrusso 2006-03-31 02:30:21 -08:00 • committed by Linus Torvalds
parent fbdf216155
commit 972410b023
6 changed files with 35 additions and 6 deletions
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6
arch/um/include/kern_util.h
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@ -116,7 +116,11 @@ extern void *get_current(void);
extern struct task_struct *get_task(int pid, int require);
extern void machine_halt(void);
extern int is_syscall(unsigned long addr);
extern void arch_switch(void);
extern void arch_switch_to_tt(struct task_struct *from, struct task_struct *to);
extern void arch_switch_to_skas(struct task_struct *from, struct task_struct *to);
extern void free_irq(unsigned int, void *);
extern int cpu(void);